It was prompted by a inquiry from Allegheny County Councilwoman Amanda Green Hawkins, who represents the district where the casino is located. She said about a dozen people had made complaints to her that "trickled in" within the past year or so. Some alleged that Rivers abruptly shut down a scheduled event or double-charged for services, each involving mostly African-American groups.

Regarding the Pittsburgh Ruff Ryders motorcycle club, the casino said the club reserved bottle service at two tables of 10 in Drum Bar for a total of 20 guests on July 21, but it turned out that they invited 400 guests to the venue -- which has a capacity of 115 -- so the bar was shut down early because of a safety risk from overcrowding.

"Although the Drum Bar party was disbursed, the Ruff Ryders were not asked to leave the casino," general manager Craig Clark wrote. "Upon notification of the Ruff Ryders' dissatisfaction, I contacted Ken Wright, met with him personally to apologize for any misunderstanding, provided a cash refund for the two table reservations and invited Mr. Wright and his group to return. Rivers Casino closely monitors all Drum Bar crowds and has discontinued bar service early in the past. In those examples and in this one, race was not a factor."

Regarding boxing events, Clark wrote that the casino has not stopped holding live matches or showing fights via satellite. "However, we have stopped hosting such events in the Drum Bar due to overcrowding and in the Wheelhouse due to vandalism and glass bottles being thrown at our screen during those events."

The banquet space or the amphitheater are the only places left for boxing, Clark wrote, and sometimes there are conflicts with previously scheduled events, as in the case of a recent Floyd Mayweather fight.

"In choosing to use an existing vendor over a new one, and choosing to relocate boxing crowds to a larger venue with less risk of property damage, race is not a factor," the letter said.

Clark's letter indicated that an Aug. 29 meeting is scheduled with Hawkins to further discuss the matter. The councilwoman has said she hasn't personally experienced racism at the casino.

Last week, casino spokesman Jack Horner released a statement that said, "Rivers Casino has zero tolerance for racism of any kind. We are meeting with the councilwoman soon and look forward to personally addressing her concerns. We are proud of our diversity track records regarding employment, service providers and community outreach."